Mastering Night Photography – Focusing

February 15th, 2015
by doinlight

A lot of people are doing nighttime photography these days including yours truly. There are many good sources of information on nighttime photography. I’ve written a few blog posts myself (Exciting Nighttime Photography in 10 Easy Steps). Nighttime photography falls into two categories – star trails and night sky. In this post I want to elaborate on something I’ve discovered recently with regards to night sky photography.

double-arch-joshua-tree-140628Nighttime photography is pretty much like daytime photography. The biggest difference is you can’t see what you’re doing. Let’s run through a quick comparison of camera settings in daytime and nighttime photography.

Mode: Aperture priority for daytime, manual for nighttime.
ISO: as low as possible for daytime, as high as possible for nighttime
f/stop: whatever gives you the depth of field you need for daytime, wide open or nearly wide open for night.
Shutter speed: whatever the camera says for daytime, 20 to 30 seconds for night.
Focus: manual or automatic focus for daytime, manual focus for night.
White balance: daylight or auto for daytime, 2800 K for night. (If you’re shooting RAW you don’t need to worry about white balance because it’s easily adjusted in Lightroom.)

The basic configuration, then, for night shooting is your widest lens at its widest or next to widest f/stop, very high ISO and shutter speeds in the 20 to 30 second range. The other thing I do is turn on ‘High ISO noise reduction’ in my camera.

Focusing at Night

Apart from manipulating all your camera controls in total darkness, the biggest challenge is focusing. Interesting nighttime photographs like their daytime counterparts have interesting foregrounds. But focusing in the dark is in itself a challenge not to mention concerns about depth of field.

In the past I’ve tried focusing on the brightest star in the sky using live view magnified 10 times but it can get a very tricky to find the little bugger. And setting your lens on infinity doesn’t always work because each lens is different and infinity may or may not actually be infinity.

If you have a very bright flashlight you can try illuminating a foreground object and focusing on it using live view. If you can get it bright enough so that live view can actually detect it, that works pretty well. But if you don’t have a light source that’s bright enough then you have to resort to trial and error. Set your lens on infinity, take an exposure and check it on your LCD screen (at its highest magnification of course). If the exposure is off make a slight adjustment and reshoot. Keep doing this until you get it in focus. It may take a while but it’s doable.

Depth of Field

But what about depth of field you ask? That brings up my big discovery that I want to share with you. Depth of field is the same at night as it is during the day. It’s determined by the optical properties of the lens which are the same in light and dark situations. The wide-angle lenses that we shoot with, even when shooting wide open, have impressive depths of field, especially if you’re shooting with a full frame sensor. Here are a few examples.

Full frame sensor
Focal length:
24 mm
Aperture: f/2 .8
Hyperfocal distance: 23 feet
Near depth of field distance: 12 feet

What this means is if you focus on something 23 feet from your lens everything from 12 feet to the stars at infinity are in focus. If you have a 16mm lens the picture gets even better (pun intended).

Full frame sensor
Focal length
: 16mm
Aperture: f/2 .8
Hyperfocal distance: 10 feet
Near depth of field distance: 5 feet

But this assumes that you can find something at the hyperfocal distance to focus on. And it also assumes that you can illuminate it bright enough so that you can see it in live view. But let’s assume that that’s not an option. Our next option is to find the brightest star in the sky and focus on it using live view. In that case your focal distance is infinity but the real question now is what did that do to the depth of field and what is the near depth of field distance. As it turns out with a full frame sensor the answer is a pretty good one. With a 24 mm lens the near depth of field distances 21 feet. With the 16mm lens the near depth of field distances is 10 feet. So if your foreground object is at least 20 feet away with a 24 mm lens or 10 feet away with the 16mm lens it will be in focus.

But what about crop sensors? The picture is not quite so rosy but the concept is still the same and actually, it’s not that bad either. Here are the figures for crop sensor.

APS-C sensor
Focal length
: 24 mm
Aperture: f/2 .8
Hyper focal distance: 37 feet
Near depth of field distance: 19 feet

APS-C sensor
Focal length: 15 mm
Aperture: f/2 .8
Hyper focal distance: 15 feet
Near depth of field distance: 7.5 feet

If you have to focus on a star with a crop sensor then with a 24 mm lens your near depth of field distance is 33 feet and with a 15 mm lens it is 14 feet. That still gives you a lot of leeway as far as foreground objects are concerned when composing your shot.

And keep this in mind. The depth of field picture only gets better if you can stop down one stop from f/2 .8 to f/4.

So focusing, while still challenging at night, is not as difficult as we first thought because depth of field comes to our rescue. The technique I use now is to focus during the day with the focal length and f-stop that I’ll be using at night and checking my lens to see where the focus distance is set relative to the infinity mark. Then at night I just adjust the focusing ring to set the focus distance back to the same setting and I’m ready to go.

One final thought.  To get the most stars in your shot it is still best to focus on them, to focus at infinity, and rely on depth of field to bring your foreground object into focus.

Night photography is a lot of fun and it’s even more so if you can bypass the anxiety of trying to get a sharp focus. And when you finally get a great foreground with the Milky Way raising above it you know you have something very exciting.

joshua_tree_140927__SM32717-Edit


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Posted in How To, Journal, Night photography | Comments (2)

  • PS I took screen shots of you original post.

  • Harold says:

    Thanks Ralph, more good practice advice. I am now in Moab and hope to try some night photography while here.

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